As the play opens, there is much merrymaking and festivity in preparation for the play. Sources suggest that the sheer happiness of all of the colorful characters is transferred to the reader almost instantly.
The mood is portrayed very well as being light and bubbly, an overall good feeling.
Cyrano's actions and the resulting emotional response from the reader, then, portray him as an individual. During this age of romanticism, this was considered to be the "chic" thing to do.
As the play progresses, we are shown various incidents in the play which elicit emotional responses from the reader: the longing Cyrano has for Roxane; his belief that he can never have her because of his appearance; a comical intervention as Christian gets a nose up on Cyrano; Cyrano and Christian working together to court Roxane; the author of the letters to Roxane being unknown to her; the passionate speech which Cyrano delivers to Roxane from behind the shrub; the existence of the cadets in such grim conditions; the death of Christian; the final resolution of Cyrano's love for Roxane and his death.
These emotions are what define the play and make it great.
Here's a list of important facts about Edmond Rostand's Cyrano de Bergerac, including setting, climax, protagonists, and antagonists shared by Sparknotes.com.